How do you solve UTF-8 Validation on LeetCode?

UTF-8 Validation (LeetCode #393) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: Understanding the bit manipulation is crucial for identifying the number of bytes in UTF-8 encoding.

What is the brute force solution for UTF-8 Validation?

The brute force approach for UTF-8 Validation is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves checking each byte in the input array to see if it follows the UTF-8 encoding rules. We will iterate through the array and validate each byte based on the expected number of continuation bytes. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve UTF-8 Validation?

UTF-8 Validation uses the following concepts: Array, Bit Manipulation. The recommended patterns to study are: Bit Manipulation, Array.

What are the interview tips for UTF-8 Validation?

Always explain your thought process clearly as you work through the problem. Be mindful of edge cases, such as arrays that are too short to contain valid characters. Practice bit manipulation problems to become comfortable with the concepts.

What are common mistakes when solving UTF-8 Validation?

Not correctly identifying the number of bytes based on the leading bits. Failing to check continuation bytes properly, leading to false negatives.

#393

UTF-8 Validation

Medium

ArrayBit ManipulationBit ManipulationArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(1)

💡

Intuition

Time O(n)Space O(1)

The optimal solution processes each byte in a single pass, checking the leading bits to determine the number of bytes in the current character and validating the continuation bytes accordingly. This reduces the time complexity significantly.

⚙️

Algorithm

5 steps

1Step 1: Initialize an index to track the current byte being processed.
2Step 2: Loop through each byte in the data array.
3Step 3: Determine the number of bytes for the current character based on the leading bits.
4Step 4: Validate the required continuation bytes based on the number of bytes determined.
5Step 5: If any validation fails, return false. If all bytes are processed successfully, return true.

solution.py27 lines

1# Full working Python code
2
3def validUtf8(data):
4    i = 0
5    while i < len(data):
6        byte = data[i]
7        if (byte & 0x80) == 0:
8            # 1-byte character
9            i += 1
10        elif (byte & 0xE0) == 0xC0:
11            # 2-byte character
12            if i + 1 >= len(data) or (data[i + 1] & 0xC0) != 0x80:
13                return False
14            i += 2
15        elif (byte & 0xF0) == 0xE0:
16            # 3-byte character
17            if i + 2 >= len(data) or (data[i + 1] & 0xC0) != 0x80 or (data[i + 2] & 0xC0) != 0x80:
18                return False
19            i += 3
20        elif (byte & 0xF8) == 0xF0:
21            # 4-byte character
22            if i + 3 >= len(data) or (data[i + 1] & 0xC0) != 0x80 or (data[i + 2] & 0xC0) != 0x80 or (data[i + 3] & 0xC0) != 0x80:
23                return False
24            i += 4
25        else:
26            return False
27    return True

ℹ

Complexity note: The complexity is O(n) because we only traverse the array once, checking each byte and its continuation bytes in a single pass.

1Understanding the bit manipulation is crucial for identifying the number of bytes in UTF-8 encoding.
2The leading bits of each byte dictate how many continuation bytes are expected.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.